SPN summary for the finale:

"There are two distinct episodes in this two-hour fire-and-brimstone buffet event. For the appetizer, "Let It Bleed," Dean faces his worst nightmare when Lisa and Ben are unexpectedly abducted. In the main course finale, "The Man Who Knew Too Much," the war in Heaven comes to a head. Castiel faces off with Raphael and the walls holding back Sam's memories of Hell crumble. Someone (human? angel? demon?) will die and someone will be transformed. Prepare to gasp, possibly cry and write angry forum entries. Oh, and sorry, John Winchester won't show his face for the finale."

Man, they better not fridge Lisa.

Seems that fridging Lisa would be too obvious a choice. I doubt they'll go there. But I'm guessing Castiel may be the one to kick Sam's wall down as a way to distract Dean and keep them from pursuing the truth. However I wonder if the transformation is Sam's as a result of the wall coming down.

So many ways this could go.

I think Castiel so far is still a little too invested in Winchester goodwill to deliberately hurt Sam like that. Making Sam a vegetable, versus telling Dean the truth? I don't see Cas coming back from making that choice--in Dean's eyes or the audience's. And I'd be surprised if the writers were going to make him that irredeemable, even if they were going to make him a bad guy.

A transformation could be a fallen angel.

A transformation could be a fallen angel.

Ooooh... I hadn't consider that!

But by transforming Sam, I was thinking that Sam may not necessarily become a vegetable. They've been implying that that would be the outcome, but I wonder if that is the only possibility when the wall comes down.

Well, I'm assuming they'll put him back together, but if Cas deliberately did something Death said would result in vegeta-Sam, I can see Dean having a really hard time getting past that, as would I.

Seems that fridging Lisa would be too obvious a choice.

Not to mention it would leave Ben floating about needing a home and a parental figure. I don't think I want to see a season of the Winchester brothers criss-crossing the country with Ben in the backseat.

I'd like to think Dean has more sense than that. Either he leaves the game and raises the kid, or someone else raises the kid. He's already been clear he doesn't want to rerun John Winchester.

Either he leaves the game and raises the kid, or someone else raises the kid.

He's definitely responsible enough to do what's best for the boy. He's made that clear. But theoretically speaking, if he were to leave the hunt so he could stay home and raise Ben, that would pretty much kill off our Show right there, wouldn't it? And having someone else raise the kid so Dean could be free to leave with Sam would be like the situation he's got now, only magnified immeasurably since he'd be the sole remaining parental unit. The guilt would kill him. (We assume he's the only parent. Where is this kid's bio-father, anyway?)

I think the guilt of raising him in the game would kill him too, so I don't see the show continuing that way either.

Right. So if the writers reason the same way we do, no one will be fridging Lisa.